1. Field of the Invention
This invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery of the coin type.
2. Description of the Related Art
In electronic equipments subject to carrying, e.g., an electronic calculator or an electronic wrist watch, etc., in order to allow the entirety of the device to be as compact as possible in dimension, a battery serving as a power supply is also required to be as small as possible in dimension and to be light in weight, and to have a sufficient discharge capacity tolerable for long use. As a power supply for such electronic equipments, so called a coin type non-aqueous electrolyte battery comprising a cathode can, a cathode pellet, a separator, an anode pellet, and an anode can stacked in order recited has been conventionally used.
Meanwhile, a coin type non-aqueous electrolyte battery as described above ordinarily has a primary battery specification. However, in recent years, since such a coin type non-aqueous electrolyte battery is being used as an electronic wrist watch or various memory backup power supplies for which long time of 5 to 10 years use is required, it has been required in various fields to proceed with a development of a rechargeable secondary battery specification in order that such a coin type non-aqueous electrolyte battery can be economically used for a long time.
As a battery to meet with such a requirement, the spotlight of attention is focused on a lithium secondary battery using lithium as the anode. However, up to the present, it cannot be said that this lithium secondary battery is at a practically acceptable level. Namely, lithium is crystal-grown in the form of dendrite with repetition of charge/discharge cycle, and is passed through holes of the separator or gaps of the fiber to reach the cathode, resulting in the drawback that an internal short-circuit takes place, or lithium is inactivated and is separated out or precipitated in the form of powder. This is an obstruction to practical use.
In view of this, as a battery to solve the drawbacks with a battery using lithium as the anode, a coin type non-aqueous electrolyte secondary battery using, as the anode material, carbon material capable of doping/undoping lithium or lithium ion, such as coke, graphite, or organic high molecular burned body, etc., has been proposed. Great expectations are laid on this coin-type non-aqueous electrolyte secondary battery because there is no occurrence of lithium dendrite due to repetition of charge/discharge cycle, the battery voltage is high, and a high energy density can be obtained.
As stated above, various coin-type non-aqueous electrolyte secondary batteries have been proposed from now. However, conventional coin-type non-aqueous electrolyte secondary batteries have a tendency such that the internal resistance is high from a structural restriction. Especially, if a volume change of the cathode pellet or the anode pellet takes place by repeating charge/discharge cycle when used under a heavy load or when used at a high temperature, rise in the internal resistance is remarkable. For this reason, it is the present circumstances that it cannot be said that conventional coin-type non-aqueous electrolyte secondary batteries are not sufficiently satisfactory in the heavy load characteristic and the high temperature characteristic.